Wiring 4 LEDs with a common ground?

[Helios]

All of my electrical know how is self taught and I dont think that this will work but I am trying to figure out a solution. I need to be able to turn on 4 LEDs separately but I need to run them through 2 slip rings. To save myself from having to make what would be 16 slip rings for just these LEDs can I use a common ground?

I have sketched up a diagram to explain what I mean.

This screams wrong to me as it is basically series and parallel wiring after the drivers. If this wont work does anyone have any suggestions for how I could cut back on slip rings?

 

[djQUAN]

If you are:

-using continuous ground drivers
-or using isolated output drivers (example: mains input led drivers)
-switching the positive input supply of the drivers

it could work.

But if you can, just wire the drivers after the slip rings. Then it won't matter if you common the grounds and wire the leds independently to their drivers.

 

[Helios]

If you are:

-using continuous ground drivers
-or using isolated output drivers (example: mains input led drivers)
-switching the positive input supply of the drivers

it could work.

But if you can, just wire the drivers after the slip rings. Then it won't matter if you common the grounds and wire the leds independently to their drivers.

I will have to look into continuous ground drivers. Thanks

I thought about wiring the drivers after the slip rings, but there are two problems.

1. This will be turning extremely fast so I am trying to keep the weight down so it doesn't tear itself apart.

2. I was hoping to control the drivers output via arduino so I need a reference voltage signal.

 

[The Lightning Stalker]

Like djQUAN said, it all depends on the
type of drivers and weather they are
continuous positive or ground. Hopefully
they are not some weird combination of the
two. (High side driver with low side
current sense)

 

[Helios]

Like djQUAN said, it all depends on the
type of drivers and weather they are
continuous positive or ground. Hopefully
they are not some weird combination of the
two. (High side driver with low side
current sense)

How would I know? I may build the drivers myself but I have considered just trying to find some adjustable drivers on ebay. The trouble is that often this information is no where to be found. Would I have to look for a trace that leads directly from the input to the output of the driver? Is there an easier way to identify in the event pictures are not detailed enough?

I am building a 2 axis spinning led sphere. Someone on this forum built a 3 axis (even more slip rings) and inspired the project. Mine will be much larger though. Instead of a sphere maybe 3" in diameter mine will be nearly 20. I have it all figured out (I think) and most of the parts, except for these drivers...

 

[The Lightning Stalker]

It can be a bit tricky if there is a low
ohm resistor in series as a current sense
because a standard meter won't "see" it.
But if you take a multimeter and put it in
continudity testing mode, most of the time
it will tell what polarity is continuous.
Test the input and output wires to see if
one tests low ohms in both directions.
That one will be the continuous polarity
most of the time. It would be a good idea
to then smoke test it on a test load before
attaching anything expensive or that has to
come in mail order. Hope this helps :beer:

 

[rhd]

You can use almost any driver topology with an added current sense monitor like the ZXCT1009 and you have a common ground driver

 

[Flaminpyro]

I would put all the electronics in the sphere then you need to balance every thing correctly in the sphere this way you will need only one set of slip rings and you'll have
your reference voltage for the arduino if you can put most of the devices in the center then there will not be as much centrifugal force, just a thought

Good luck and please share your work with us or do a review please.

 

[Helios]

This is all great info thanks!

Pyro: are you suggesting even the arduino? That's an interesting idea as I would just need to send in power but that adds a lot to the spinning mass. The other issue is that the arduino will also control the motors which are further back in the system, so I would have to slip ring the control signal backwards...

Most of the structure including the X which makes up the sphere is wood (oak dowels mounted in a drilled block) to keep things somewhat light and be easy to work with. I may just building the led drivers and mount them on the X so that I can just send each the control signal with a common return.

Edit: obviously I would need to run power as well haha which would put me at 14 slip rungs...which isn't much of an improvement now that I think about it. I'd rather run 16 and have the drivers on a sationary board...

 

[The Lightning Stalker]

The only downside to putting everything in
the sphere (including micro) with only 2
rings for power is that it becomes
autonomous with no way to control the color
patterns from the outside. It might be
doable using IR to get data in, though.

 

[Helios]

After talking with FireMyLaser who inspired this project I will be putting as little as possible in the sphere. I would rather make more slip rings than add weight. I am also reducing it to 3 arms and leds instead of 4. I underestimated the gyroscopic forces at play so the arduino will most definitely be mounted to the baseboard.

I think the best option is to make my own continuous ground drivers and have 8 slip rings for the LEDs. The gyroscopic forces (which will already be intense) get worse the more weight you add so since its already questionable whether I will get enough speed I will be doing everything I can to cut weight.